Coating composition for paperboard comprising an aqueous dispersion of a butadiene-styrene copolymer and a hydrous aluminum silicate clay



Patented Mar. 16, 1954 COATING COMPOSITION FOR PAPERBOARD COMPRISING AN AQUEOUS DISPERSION OF A BUTADIENE-STYRENE COPOLYMER AND A HYDROUS ALUMINUM SILICATE CLAY Richard J. Rother, Breckenridge Hills, and Albert R. McManus,

St. Louis, Mo., assignors to Gaylord Container Corporation, St. Louis, Mo., a

corporation of Maryland N Drawing. Application March 25, 1953, Serial No. 344,674

6 Claims.

be packaged of the class described and a relatively weak bond with paperboard, so that when the contents becomes solidified, the container may be readily stripped therefrom, leaving the material entirely free of paperboard slivers, fragments and the like.

The usual practice in preparing asphalt, for example, for shipment and storage in containers is to render it readily flowable by raising its temperature to from 250 F. to 400 F. or higher and rapidly pouring it into the containers which are then allowed to stand until the asphalt solidifies. Packages for this purpose have been made of thin gauge metal, paperboard or other suitable materials. However, since the, packaging of asphalt for roofing purposes, manufacture of shingles and for many other purposes is a large-scale operation, the storage of metal drums and other non-collapsible containers entails a storage space problem of considerable magnitude. Paperboard containers consequently have important advantages over metal containers due to their lower cost and the fact that they may be shipped to the user and stored in collapsed form, requiring a minimum of storage space prior to transfer to the loading line.

The use of paperboard containers for packaging materials of the class described in liquid form involves difiicult problems since these materials tend to penetrate paperboard, so that in the absence of an effective barrier between the walls of the container and the hot materials, leakage of the latter may result. In addition, such materials are quite tacky at elevated temperatures and strongly adhere to paperboard, so that it is virtually impossible to strip the container from the-solidified contents without leaving highly objectionable adhering strips, slivers and particles of paperboard embedded therein. Such extraneous materials render asphalt, for example, entirely unsuitable for the purpose hereinbefore described.

Many prior types of coatings, when applied to the fiat blanks from which the containers are assembled, have a tendency to crack or flake at (Cl. Mill-17.4)

the scores when the blank is scored and assembled and allow the fluid material to penetrate and strongly adhere to the board with the consequence that strips, slivers and particles of the latter remain embedded in the solidified asphalt when the container is removed therefrom.

A principal object of the present invention is to provide a coating composition for applying to the inner surfaces of paperboard containers which effectually prevents penetration 01' bituminous and similar tacky materials at elevated temperatures into and through the board and which adheres but slightly to the board, so that upon solidification of the contents, the container may be cleanly and readily removed, leavthe solidified material entirely free of contaminating particles of paperboard.

Another object is to provide a coating composition which may be applied as a single coat to a flat paperboard blank suitable for assembling into a container for packing asphalt and similar bituminous materials which provides an effectual barrier to penetration of and adherence to the container of materials of the kind described at elevated temperatures.

Still another object is to provide a coating composition which may be applied in a single coat to the interior surfaces of a paperboard asphalt drum which forms with liquid asphalt contained therein and a substantially negligible bond with the paperboard container.

A further object is to provide a process for preparing a composition suitable for coating the interior surfaces of paperboard containers for shipping and storing asphalt and other bituminous material.

The invention, therefore, comprises a unique composition adapted to form a barrier on the interior surfaces of paperboard containers which is impervious to liquid asphalt and other bituminous materials and adheres relatively weakly to the paperboard, whereby the latter may be cleanly stripped from the contents upon solidification thereof.

The coating consists of an aqueous composition of about solids comprising the following ingredients, expressed in parts by weight, compounded in the order set forth:

Step 1.Into a tank of suitable size, equipped with agitation, preferably of a type designed to avoid entrainment of air into the mixture, about 76 gallons of water are introduced at a tempera-.-. ture of about F. to F., or raised to that level after the introduction if means for heating the Water in the tank are available.

Step 2.-About 13 pounds of sodium alginate a very strong bond are dispersed in about 28 gallons of water and added to the tank and agitation of the mixture is started and continued throughout the additions and compounding of the subsequently added ingredients. It is preferred to use a form of sodium alginate as low in viscosity as possible. A satisfactory commercially available brand is marketed under the name of Kelgin Xi, though other types of the material may be used.

Step 3.--About 3 pounds of sodium hydroxide dissolved in about 4 gallons of water are added to the circulating mixture.

Step 4.Approximately 2000 pounds of a hydrous aluminum-silicate type of clay are sifted into the tank as rapidly as possible and the agitation continued until all lumps have been broken down and a smooth, homogeneous mixture is attained. This will usually require 30 to 60 minutes,

depending upon the emciency of the agitating equipment. About 4 or 5 gallons of water are used to rinse the agitator paddles free of the mixture.

Suitable types of commercially available clays are known by the tradenaznes Klondike, DRG and Kaolex.

Step 5.-Approximately 385 pounds of an aqueous emulsion of the GR-S type of synthetic rubber containing approximately 56% solids in about 9- gallons of water are added and mixed for approximately one hour.

It is desirable that the ratio of the butadienestyrene copolymer of the GR-S emulsion be about 4'5 to 55 for the most satisfactory performance of the coating composition. A commercial brand,

known as Chemigum 101A of about 58% solids content is very satisfactory, although somewhat higher ratios of styrene and correspondingly lower ratios of butadiene may be employed if desired, for example, a ratio of 40 parts of butadiene to 60 parts of styrene, depending on the characteristics of the paperboard to which the coating is to be applied.

The addition of the synthetic rubber emulsion completes the preparation of the coating composition. The quantities set forth will produce approximately 285 gallons of coating composition having a solids content of about 65% to 66%.

l The pH of the composition will be between about 10.0 and 10.5.

The composition may be given a distinctive color if desired by incorporating a dye therein, preferably following Step 1 of the process and before the addition of the sodium alginate. For example, 15 to 18v pounds of a black dye may be dissolved in the initial charge of water. A suitable dyefor the purpose is Nigrosine WSB but various other water soluble dyestuffs may be employed if desired.

The coating may be readily applied to the paperboard container by spraying, brush or other convenient means, but is preferably uniformly applied to the unscored roll stock on a standard coating machine.

The coating sets on the paperboard rapidly and due to its elasticity characteristic, will not crack or otherwise fail at the score lines when the contain er blank is assembled.

As hereinbefor mentioned, while the coating forms a relatively weak bond with the paperboard, it does, indeed, provide an impermeable barrier to hot asphalt or other bituminous materials and most efiectit'eiy rrevents penetration thereof into thepaperb-oarcl. On the other hand, the coating forms a very strong bond with the asphalt, so that upon cooling, the paperboard may be readily and cleanly stripped from the solidified asphalt, while substantially all of the coating is retained by the asphalt. The portion of the coating retained by the asphalt is entirely unobjectionable for the hereinbefore described uses.

The invention, therefore, permits the packing, storing, and shipment of asphalt in extremely economical, collapsible paperboard containers or drums when coated with the hereinbefore described composition and eliminates contamination of the solidified asphalt by embedded particles and adhering slivers of paperboard when the containers are removed from the asphalt at the point of use.

What we claim is:

1. A homogeneous, aqueous coating composition, adapted to form a barrier to penetration of asphalt and other bituminous materials in the liquid state when applied to the interior surfaces of paperboard containers, said composition comprising the following admixed ingredients: about 122 gallons of water, about 13 pounds of sodium alginate, about 3 pounds of sodium hydroxide, approximately 2000 pounds of hydrous aluminumsilicate clay and about 385 pounds of an aqueous emulsion of but-adiene-styrene copolymer of approximtely 56% solids content in the ratio of from 45 parts of butadiene and parts of styrene to 40 parts of butadiene and parts of styrene.

2. The composition set forth and claimed in claim 1 wherein 15 to 18 pounds of a water soluble dyestuff is incorporated in the composition to impart a distinctive color thereto.

3. The composition set forth and claimed in claim 2 wherein the dyestufi is sulfonated nigrosene.

4. The process of compounding a homogeneous, aqueous coating composition adapted to form a barrier to penetration of bituminous materials in a liquid state when applied to the interior surfaces of paperboard containers, said process comprising the successive steps of metering about 50 gallons of water into a mixing tank, equipped with agitators, raising the temperature of the water to about F. to F., adding about l3 pounds of sodium alginate dispersed in about 28 gallons of water under agitation, adding approximately 3 pounds of sodium hydroxide dissolved in about 4 gallons of water to the circulating mixture, introducing from 1950 to 2050 pounds of hydrous aluminum-silicate clay as rapidly as possible, adding about 5 gallons of rinse water, and continuing the agitation for 30 to 60 minutes until a smooth, homogeneous mixture is attained, introducing approximately 385 pounds of an aqueous emulsion of butadiene-styrene copolymer of about 56% solids content and about 9 gallons of water and continuing the agitation for approximatelyone hour, the ratio of butadiene-styrene of said emulsion being within the range of 45 parts of butadiene and 55 parts of styrene to 40 parts of butadiene and 60 parts of styrene.

5. The process set forth and claimed in claim 4', wherein from 15 to 18 pounds of a water soluble dyestuff to impart a distinctive color thereto is added to the initial charge of water before the addition of the sodium alginate.

6. The process set forth and claimed in claim 5 wherein the water soluble dyestuif is sulfonated nigrosene.

RICHARD J. ROTHER. ALBERT R. McMANUS.

No references cited. 

1. A HOMOGENEOUS, AQUEOUS COATING COMPOSITION,ADAPTED TO FORM A BARRIER TO PENETRATION OF ASPHALT AND OTHER BITUMINOUS MATERIALS IN THE LIQUID STATE WHEN APPLIED TO THE INTERIOR SURFACES OF PAPERBOARD CONTAINERS, SAID COMPOSITION COMPRISING THE FOLLOWING ADMIXED INGREDIENTS: ABOUT 122 GALLONS OF WATER, ABOUT 13 POUNDS OF SODIUM ALGINATE, ABOUT 3 POUNDS OF SODIUM HYDROXIDE, APPROXIMATELY 2000 POUNDS OF HYDROUS ALUMINUMSILICATE CLAY AND ABOUT 385 POUNDS OF AN AQUEOUS EMULSION OF BUTADIENE-STYRENE COPOLYMER OF APPROXIMATELY 56% SOLIDS CONTENT IN THE RATIO OF FROM 45 PARTS OF BUTADIENE AND 55 PARTS OF STYRENE TO 40 PARTS OF BUTADIENE AND 60 PARTS OF STYRENE. 